1. Field of the Invention
This invention relates to an automatic accompaniment apparatus which is simple in construction as an auto-bass circuit having many codes and suitable for fabrication as an integrated circuit.
2. Description of the Prior Art
The circuit structure of a conventional auto-bass or auto-arpeggio circuit is shown in FIG. 1. In FIG. 1, a chord produced by an accompaniment manual keyboard 1 and is detected by a code detector 2, which then outputs a root signal and a code signal indicative of the kind of code. For example, in the case of achieving auto-bass or auto-arpeggio accompaniment in connection with five kinds of codes each representing a chord type, such as major, minor, seventh, augment and diminish, the root signal is converted by eight encoders 3 of root, 3rd.sup.b, 3rd, 5th.sup.b, 5th, 6th.sup.b, 6th and 7th.sup.b to signals corresponding to their degrees, respectively. On the other hand, a read pulse for reading out a read-only memory (ROM) 5 and an attack signal are derived from a rhythm pulse generator 4. The content of the ROM 5 is switched by the code signal from the code detector to the content correponding to the kind of code and read out by the read pulse from the rhythm pulse generator 4 to derive a select signal corresponding to the kind of the code. By the select signal from the ROM 5, the signal applied to a select circuit 6 from the encoder 3 are selected and sequentially applied to a tone gate 7. For example, if major is designated by the code signal, signals of root, 3rd, 5th, 6th and 7th.sup.b are selectively derived from the select circuit 6. The tone gate 7 passes therethrough scale signals in accordance with the signals selected by the select circuit 6, and the scale signals are provided to an envelope circuit 8, in which they are each amplitude controlled by the attack pulse from the rhythm pulse generator 4, thereafter being applied to a speaker 11 via a filter 9 and an amplifier 10.
With such a conventional construction, an increase in the kinds of codes used calls for a corresponding increase in the number of storage contents of the ROM 5, making it complicated and expensive. Further, the increase in the kind of codes causes an increase in the number of encoders 3, which increases the number of wirings and the number of bits of the select circuit 6, resulting in appreciably complex construction. Moreover, the prior art construction has the drawback that in the case of bass or arpeggio performance ranges over some octaves, octave control is difficult.
This invention is intended to overcome such defects of the prior art.